Process of producing cement and recovering potassium compounds.



V UNITED STATES PATENT curios.)

FREDERICK W. HUBER AND FRANK F. REATI-I, 0F RIVERSIDE CALIFORNIA.

PROCESS OF PRODUCING CEMENT AND RECOVERING POTASSIUM COMPOUNDS.

No Drawing.

To all whom it may concern:

Be it known that we, FREDERICK \V. Human and FRANK F. REA rII, citizens of the United States, residing at Riverside, in the county of Riverside and State of California, have invented certain new and useful Improvements in Processes of Producing Cement and Recovering Potassium Compounds, of which the following is a specification.

The present invention relates to improvements in the manufacture of cement and the recovery of by-products, particularly salts of potassium, by a method involving certain features in common with our U. S. Patent No. 1,194,344.

In the burning of Portland cement, from ordinary cement making materials, and particularly i,n rotary kilns, where a rather strong gas current is employed, there is always produced a considerable amount of flue dust, which material ordinarily carries the larger part of the alkalis and oxids of sulfur contained in the raw mix. Various processes have heretofore been proposed for the recovery of the a-lkalis contained therein, but most of these processes have not been entirely satisfactory.

The most satisfactory attempt with which we are familiar consists in mixing this flue dust with sufficient aluminous, silicious or calcareous material, or material having two or more of these properties, to produce a material suitable for use as a cement raw mix, and thereafter calcining or reburning such mixture.

This second calcination, 0r reburning, does not completely decomposethe oxids of sulfur, nor does it completely liberate the alkali metals, and two largea portion of the oxids of sulfur and salts of the alkali metals remain in the clinker. One result is that, aside from the loss of alkali metals, that the cement produced by grinding such clinker is too high in oxids of sulfur, and in alkali metals (sodium and potassium salts of oxids of sulfur) to be safe for use as cement for structural purposes.

I The following table shows analyses of va- Specification of Letters Patent.

-fluorid being, most effective material for'this'purpose.

Patented Mar. 13, 1917.

Application filed September 26, 1916. Serial No. 122,295.-

rious materials used and made, in experimentsconducted on this process:

In the above table No. 4 shows the clinker produced by burning the original dust (that is to say on material No. 2), after correcting its composition to form a normal raw mix, and it will be noted that-this material is excessively high in alkalis and oxids of sulfur.

We have now discovered that it is possible to completely decompose and liberate the oxids of sulfur and the alkali metals contained in the flue dust, by a process which involves a modification of the process above described, and certain features in common with 'our U. S. Patent No. 1,194,344 above referred to.

In this process the original law material is calcined in rotary kilns in the'ordinary manner, thereby producing cement clinker, and the flue dust so produced is recovered, which dust contains most of the alkali metals and most of the oxids of sulfur contained in the original raw mix, and those derived from fuel, and which dust may correspond substantially to the material No. 2 above described. To this material is added a substance capable of readily liberating the alkali metals in a somewhat volatile state, such a material as finely divided calcium so far as we have found, the

To the flue dust, then, is added an amount of calcium fiuorid substantially equivalent to the amount of alkali metals present in the flue dust, together with sufficient argillaceous or calcareous material (or both) to bring the composition up to that of a nor- .its'vjgrecovery an economic factor, and to mal cement. raw mix. This mixture is then No. sio,. mos. "cao. K20. Na O. s.

. 9.46 154.62 0.03 Trace. Trace.

5 Clinker. 22. 41

The flue gases were cooled, and the flue dust produced (second flue dust) was found to'contain considerable quantities of sodium 20 and potassium fluorids, some s'ulfites, sulfates, lime and other materials. To recover the fluorin from this material, we preferably add to the flue dust (if it does not already contain a sufiicient amount thereof) salts or other compounds of calcium, such as the oxid or sulfate of calcium or the like, and digest the Whole mixture with water,

preferably in a heated conditiomuntil substantially all of the fluorin present has been converted into calcium fiuorid, while substantially all of the potassium and sodium salts become dissolved, for example as sodium and potassium sulfates. The solid is then separated from the liquid, for example byafiltration or sedimentation, the liquid evaporated for the recovery of the alkali metal salts, and the solid material containing calcium fluorid, is employed for treating a further batch of the first flue dust, as above described.

- The process of particularly adapted to the preparation of cement the ordinary, raw]-,.materials whose-potassium content is suflicient to make ldspathic and other rocks of high potasus tim'content and of suitable chemical composition for cement making. 50 What we claim-is: I

1. A process of rec0ver1ng alkali f 'Q T by-products comprising finely divided "sili cious, calcareous products containing alkali salts ofsulfur-and-oxygen-containing acids, which comprises mixing sugh material'with a fluorid of an alkaline earth-metal, and then heating the mixture to a cement-forming temperature, under conditions capable of promoting the liberation and volatilization of alkali metal compounds.

dust containing materially, more alkali sulthe present invention is 2. A process of treating cementjkiln flue i fate than a normal Portland cement raw mix, which comprises mixing such dustwith a quantity of a haloid salt of an alkali earth metal, and calcining the mixture at a cement-forming' temperature.

3. The step of working up a flue dust derived from'the burning of cement, by mixing the same with a material containing a fluorid, and clinkering the mixture.

4. The process which comprises burning cement-forming materials containing alkali metal compounds, collecting the flue dust thereby produced, mixing the same with a haloid salt of an alkaline earth metal, again I calcining and collecting a second flue dust,

digesting said secondflue dust with water in. the-presence of an alkaline earth compound and thereafter separating the aqueous liquid containing at least the major portion of the alkali in the form of water-soluble compounds from the calcareous residue. 5. The process which comprises-calcining a raw cement mix containing material amounts of potash, and collecting a potassifero'us flue dust, mixing material containing calclum fluorid, calcin -ing such mixture and collecting a second flue dustytreating such second flue dust with such dust with a I water in the presence of calcium compounds,

separating the liquid from the solid ma pound from the liquid.

7 6. In the treatment of cementvflue dust,

the steps of heating such dust with a ma terial containing alkaline earth metal fluorid to vaporize alkali metal fiuorid, treating the product, with a salt of an alkaline earth metal and Water,.whereby an insoluble product containing alkaline earth metal fluorid is produced, adding such insoluble productfto, a further quantity of such flue dust, and repeating cycle of opera tions.

7. In the'manufactureof cement, the im 'provement which comprises mixing a flue dust' containing. alkali, with a sufiicie'nt quantity 'of an alkali earth fluorid to furnish fluorin equivalent for the alkali present, and with assuflicient quantity of other materials I to form a normal cementmix, and calcining the mixture .atfa cement-forming tempera- 8. In the treatment of lalkal-i;containing .flue dust, the step of calcium a mixtureterials, and recovering a potassium come comprising such-a dust, an al aline earth 'metalfluorid' and such other materials as may be necessary to produce a substantially I normal cement mix.

In testimony whereof we afiix our signa- .t'uresL FREDERICK W. HUBER. K: 

